Method for detecting the presence and concentration of weak acids and bases in liquids

ABSTRACT

The concentration of weak acid and weak base constituents, or their soluble salts, in liquids is determined by passing succeeding samples of constant volume to a separation zone wherein target constituents are volatilized by reagents, then volatilized analytes are stripped from the liquid matrix and carried to a detection zone at a constant flow rate, wherein signals proportional to the variations in individual target analyte concentrations between succeeding samples are generated.

BACKGROUND OF THE INVENTION

This invention relates to novel apparatus and methods useful fordetermining the concentration of weak acid or weak base components, ortheir soluble salts, in liquids containing such acid, base or salt.

It is well known that it is useful to be able to determine theconcentration of weak acid and base constituents, or their solublesalts, in liquids for the purpose of monitoring and controllingprocesses. Weak acids are characterized as being partially ionized inwater solutions (i.e., H₂ S, CO₂, HCN and CH₃ CO₂ H), in contrast tostrong acids which are fully ionized in water (i.e., H₂ SO₄). Weak bases(i.e., NH₄ OH) can be similarly distinguished from strong bases (i.e.,NaOH). Salts are produced by the reaction between acids and bases.Soluble salts are capable of mixing with liquids to form solutions. Forexample, the reaction between H₂ S, an acid, and monoethanolamine, abase, produces monoethanolamine bisulfide, a soluble salt. Unlessotherwise indicated, any reference to detecting weak acid and basecomponents in this application should be deemed to encompass detectionof the soluble salts of such weak acid or base, if any. Determination ofthe concentration of weak acid and base constituents, or their solublesalts, in liquids is useful in, but in no way limited to, amine systemcontrol and waste water treatment. Of particular importance is thecontinuous on-line measurement of the quality of industrial processstreams containing weak acid and base components, or their solublesalts.

Amine system control methods based on the measurement of H₂ S in richamine are taught, for example, in U.S. Pat. Nos. 3,958,943 and 4,289,738which are hereby incorporated by reference and made a part hereof.Typically, liquid amine is used to remove acid impurities, such ashydrogen sulfide and carbon dioxide, from gas. The amine is contactedwith the gas so as to cause the impurities to be absorbed by the amine.Then the amine is regenerated by stripping acid gases out, leaving alean amine that is suitable for recontacting with gas. Stripping isaccomplished by heat input or pressure decrease. The degree to whichacid gases are stripped from rich amine depends on the amount of heatused or the pressure drop. Over-stripping, or removing more acid gasthan necessary to regenerate amine, results in an energy penalty. On theother hand, government regulations limit the maximum amount of of SO₂that may be generated when gas is combusted. Since SO₂ is generated whenH₂ S is burned, understripping (removing too little acid gas) can resultin environmental penalities or unsalable gas.

An optimum amount of acid gas should be removed from amine to avoidunderstripping yet minimize energy costs. Prior art teaches that aminesystem heat input should be based on the amount of hydrogen sulfideabsorbed by the amine: the greater the amount of acid gas absorbed, themore heat input required to liberate the acid gas from the amine.Clearly, the importance of determining the concentration of weak acidsin liquids is well known.

Increasingly strict environmental regulations have made it vital toprevent prohibited discharges from waste systems. To this end, theusefulness of monitoring waste water for NH₃ content is well known. WhenNH₃ content exceeds acceptable levels, the water can be diverted tobuffer storage away from waste treatment systems thereby avoiding upsetof the treatment process. In addition, neutralization of foul water bythe addition of treating chemicals can be optimized using control basedon the monitoring of weak base constituents dissolved in the water.

A review of the art reveals that limited means are presently availableto achieve the desired determinations. Hydrogen sulfide detection may beattempted using several commercially available analyzers. However, nocommercially available instrument is capable of essentially continuouson-line analysis of hydrogen sulfide and carbon dioxide. Furtherdisadvantages of present analysis apparatus include: uncorrected drift,inability to distinguish interfering components from analytes andanalyzer response that is adversely affected by pH, color, turbidity andtemperature. As a result, commercially available hydrogen sulfideanalyzers lack the degree of accuracy and repeatability necessary forcontinuous on-line measurement.

A method for determining the concentration of a carbonate and a sulfitein a liquid is disclosed in U.S. Pat. No. 4,663,724. A commercial deviceemploying the teachings of the '724 patent is not available. The methodinvolves calculating the concentrations of CO₂ and SO₂ in a liquid basedon the concentrations of CO₂ and SO₂ determined for a continuouslyflowing sample stream, the flow rate of the sample stream and the flowrate of a carrier gas. It remains to be seen whether the '724 disclosureis practical since it relies on calculations which are very sensitive toflow measurement inaccuracies.

As previously mentioned, for amine system control it is useful to knownot only H₂ S content of amine, but also CO₂ content. While the reasonsfor this are described below in detail, at this point it is sufficientto say that, in general, H₂ S represents only a fraction of the totalacid gas present in lean amine. Therefore, total acid gas is a bettermeasure of lean amine quality so that H₂ S and CO₂ content should bothbe used to control regeneator heat input. Not only is instrumentationpresently unavailable to make these determinations, but there is ageneral lack of appreciation in the art for the importance of measuringtotal acid gas content in amine streams used to remove impurities fromgas.

The shortcomings of the art present those in processing industries witha dilemma. The usefulness and desirability of having detection apparatusand methods for continuous determination of the concentration of weakacid and base constituents dissolved in liquids is recognized, yetsuitable devices and methods have not been developed to achieve thistype of on-line analysis. As a result, it is customary in amine systemcontrol, for example, to obtain samples for analysis once per shift. Thetime lag between obtaining samples, transporting them to centrallaboratory facilities and performing analyses frustrates the effectiveutilization of analysis results in process control. By the time processoperations are modified based on this sample analysis, conditions havealready changed. While such time lag in obtaining analysis resultsimpairs continuous feedback process control, it is fatal to mostcontinuous feed-forward process controls. This is because feed-forwardsystems adjust downstream operating conditions in response to variationsin upstream influent quality. The determination of influent quality mustbe on-line and continuous in such a system.

Similarly, typical waste treating control involves capturing samples foranalysis in a laboratory. Water treating chemical addition rates may bebased on analysis performed as infrequently as once per month. The timelag between sampling and process control using analysis results impairseffective upset prevention and causes uneconomical treatment of wastewater.

SUMMARY OF THE INVENTION

The present invention overcomes the problems and disadvantages of theprior art by providing a method and apparatus for on line determinationof the concentration of weak acid or weak base components of one or moreliquid streams. Substantially all of the acid or base components of eachof a plurality of individual, succeeding liquid samples of essentiallyconstant size are volatillized by contact with a reagent in a separationzone. The volatilized analytes are stripped from the liquid matrixwithin the separation zone by means of an analyte carrier stream whichflows at a substantially constant rate. Volatilized analytes aretransported to a detection zone by the analyte carrier stream. Theconcentration of volatilized analytes is determined in the detectionzone and a control signal proportional to analyte concentration isgenerated. These signals may be used for a variety of quality analysisand process control functions.

Samples are introduced into the separation zone by means of a samplecarrier stream which flows from a sample port to the separation zone.The continuously flowing sample carrier one sample away from the sampleport before succeeding samples enter the stream. Liquid or gas phasesample carrier fluids may be employed. Sample carrier fluids may reactchemically with sample components unless such reaction interferes withthe smooth flow of sample carrier. Where separation reagent is used assample carrier fluid, the sample carrier steam itself is part of theseparation zone. Where an inert sample carrier fluid is used (i.e., afluid which does not substantially chemically react with targetconstituents), the sample carrier stream is not part of the separationzone.

Reagent may be introduced into the separation zone as sample carrierfluid or through a separate reagent inlet into the separation zone. Inthe case of target acid constituents (including soluble salts of acids),volatilization is achieved using a strong acid reagent such as 10 Nsulfuric acid. When base constituents or their soluble salts aretargeted, a strong base reagent, such as 10 N sodium hydroxide, is used.Volatilization may occur as a result of a reaction between targetconstituents and reagents (i.e., bisulfides in a sample will react withsulfuric acid to form H₂ S), or through a dissociation process where theresulting volatilized analyte is the same species as the targetconstituent (i.e., carbon dioxide dissolved in an amine solution).

Volatilized analytes may be entrained in liquids within the separationzone, although it is likely that a portion of the volatilized analyteswill spontaneously migrate from the liquid to a vapor space within theseparation zone. Entrained volatilized analyte is separated from theliquid by means of upwardly flowing gas bubbles. The gas flows into theseparation zone from an analyte carrier stream inlet which is locatedbelow the liquid level inside the separation zone. Generally, analytecarrier gas is inert (i.e., does not substantially chemically react withthe other contents of the separation zone), however, analyte carrier gasmay be selected so as to react chemically with volatilized analytesresulting in a more readily detectable analyte species. The separationzone is configured so that any volatilized analyte separated from theliquid is carried by the analyte carrier gas from the separation zone tothe detection zone through a vapor outlet.

A variety of detection devices may be used to determine the amount ofanalyte released from the sample matrix. For example, gas phasedetection of CO₂ and h₂ S can be achieved using spectrophotometricdetectors. The Model No. IR-703 infrared analyzer, manufactured byInfrared Industries, Inc., of Santa Barbara, Calif., is one such devicewhich is capable of gas phase measurement of CO₂. The Model No. 400Photometric Analyzer, manufactured by the E. I. du Pont de Nemours &Co., of Wilmington, Del., is one such device which is capable of gasphase measurement of H₂ S. Liquid phase detection NH₃ can be achievedusing conductivity detectors. Gaseous NH₃ removed from the sample matrixis allowed to diffuse in a liquid stream using, for example, a PN 85-705diffusion cell, manufactured by FIAtron Process Systems, Inc. (FIAtron)of Oconomowoc, Wis. The FIA-Duct 500 Conductivity Detector, alsomanufactured by FIAtron, is but one commercially available instrumentwhich is capable of liquid phase measurement of NH₃.

It is critical that the following conditions be met in order for themethod and apparatus described herein to perform properly:

1. the amount of unreacted reagent in the separation zone must bemaintained at a concentration sufficient to cause substantially completevolatilization of analytes each time succeeding samples are introducedinto the separation zone; and

2. each succeeding sample must be of essentially constant volume; and

3. the rate at which analyte carrier gas passes through the separationzone to the detection zone must be essentially constant.

Also important, but not as critical (acceptable approximate tolerancesare indicated in parentheses), the following conditions enhance theeffectiveness, accuracy and repeatability of the invention:

1. succeeding samples, as well as the separation zone itself, shouldremain at a relatively constant temperature (i.e., ±20° F.);

2. succeeding samples should be introduced into the sample carrierstream at relatively constant time intervals (i.e., within ±25% of setpoint);

3. the flow rate of the sample carrier stream should be relativelyconstant (i.e., within ±10% of set point);

4. the flow rate of reagent into the separation zone through the reagentstream inlet should be relatively constant (i.e., within ±10% of setpoint); and

5. the volume of liquids within the separation zone should be relativelyconstant (i.e., within +5% of set point). While some variation istolerable, in the practice of the invention it is rare that there ismuch deviation in the volume of liquids in the separation zone. This isprimarily due to the configuration of the separation zone, as describedin greater detail below.

By meeting all of these conditions, it is possible to substantiallylimit the number of system variables to one: the concentration of targetconstituents in the liquid stream from which samples are taken. Thoseskilled in the art of process analytical instrumentation will understandthat it may be possible to alter one condition if an appropriatecountermeasure is taken. However, the preferred embodiment of the methoddescribed herein incorporates the above conditions thereby achieving themost economically improved practice of the invention.

The pulsed nature of the concentration determinations is exploited formonitoring potential detection instrument drift. For instance,spectrophotometric detectors can be calibrated to a baseline readingwhen only analyte carrier gas is present. As volatilized analytes passthrough the detectors, "peaks" occur which represent the amount ofradiation absorbed by the analytes. Between peaks, absorbancemeasurements should return to the baseline reading. "Peak" output fromthe detector can be used to determine analyte concentration while"baseline" output occurring between peaks can be used to verify that thedetector drift has not occurred. Depending on the degree of accuracydesired, instrument maintenance alarms can be triggered when baselinedrift exceeds allowable limits.

Improved amine system control can be achieved by inputting only as muchsteam into an amine regenerator as is required to achieve desiredleanness. Control of steam input is based on continuous determination ofacid gas content of amine, both before and after regeneration, using,for example, analysis methods and apparatus disclosed herein.

Water treatment improvements can be achieved, for example, by usinganalysis methods and apparatus disclosed herein to continuously monitorammonia levels in waste water. For instance, various water treatmentmethods employ microorganisms to digest organic waste. Themicroorganisms require nitrogen and other nutrients to grow. Ammonia inwater treatment system influent represents a source of nitrogen,although excess ammonia (i.e., levels above microorganism nutritionalrequirements) will pass through the system, sometimes causing permitlevels to be exceeded. Such excursions can be prevented by divertingwaste water with excess ammonia to buffer storage, then feeding it intothe treatment system when influent conditions change. It is important,therefore, that ammonia in influent be monitored so that microorganismnutritional requirements can be satisfied and, at the same time, so thatpermitted ammonia levels for the discharge of treated water can be met.In addition, pretreatment of waste water (i.e., pH control) would costless, both in terms of equipment and chemicals consumed, if performed ona continuous basis using automatic control rather than by batch as istypical at present. Continuous control requires continuous on-linedetermination of acid or base in water.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one embodiment of the invention,and together with the description serve to explain the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an improved apparatus and method fordetermining the concentration of weak acid and base constituentsdissolved in liquids.

FIG. 2 is a cross-sectional schematic view of the internal elements of aseparation chamber that is a part of the apparatus and method set forthin FIG. 1.

FIG. 3 is a diagram showing a simplified typical amine contactor andregeneration system.

FIG. 4 is a graph showing that hydrogen sulfide represents only afraction of the total acid gas in lean amine.

FIG. 5 is a graph showing the nominal concentration of H₂ S by weight ina sample versus the detector concentration of H₂ S by weight determinedusing the invention.

FIG. 6 is a graph showing the nominal concentration of CO₂ by weight ina sample versus the detector concentration of CO₂ by weight determinedusing the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 of the drawings, there is shown a system which canbe used for carrying out a method embodying this invention. A samplestream 4 leads from liquid stream 2 through sample flow indicator 6 tosample port 8. At the same time, carrier fluid stream 12 flows from asource not shown at a flow rate indicated and controlled by carrierfluid flow indicator and controller 14 to sample port 8. Sample port 8,preferably a six port valve, such as the commercially available ModelNo. 3527330 manufactured by Combustion Engineering of Lewisburg, W. Va.,is effective to capture samples of constant size from sample stream 4and deliver these samples into carrier fluid stream 12 which, uponexiting from sample port 8, flows through sample carrier stream 18 intoseparator vessel 20. It is critical that the samples of the processliquid be of essentially the same size. Liquids delivered to sample port8, but not used for sampling, is returned to liquid stream 2 throughsample return stream 16. In this manner, the liquid flowing throughsample stream 4 is maintained to be representative of the liquid flowingat essentially the same time through liquid stream 2.

Referring to FIG. 2, the configuration of separator vessel 20 can beseen in greater detail. Separator vessel shell 26 is an enclosure whichis airtight with inlets for sample carrier stream 18, reagent inletstream 32, described in more detail below, and analyte carrier stream50, also described in more detail below, and outlets for separatorvessel drain 22 and separator vessel vapor outlet stream 40 described inmore detail below. Liquids container 24 is positioned inside separatorvessel shell 26. During normal operation, liquid flows into liquidcontainer 24 through sample carrier stream 18 and reagent inlet stream32. Liquid overflowing the liquid container 24 collects inside separatorvessel shell 26 and flows down separator vessel drain 22. Separatorcolumn 28 is an extension of separator vessel vapor outlet stream 40extending from the top of separator vessel shell 26 down into liquidcontainer 24. Analyte carrier gas, samples, sample carrier fluid andreagent mix in stripping zone 27 within separator column 28. It iscritical that the flow rate of analyte carrier gas into separator vessel20 be sufficient to ensure that volatilized analytes from one sample arestripped and purged from separator column 28 before succeeding samplesare introduced thereto. Gases accumulating inside separator vessel shell26, but outside separator column 28, are discharged from separatorvessel 20 through separator vessel drain 22. Separator column 28 extendsfrom separation vessel vapor outlet stream 40 to well below the liquidlevel inside liquid container 24. Sample carrier stream 18 and reagentinlet stream 32 flow into separator column 28 within stripping zone 27.Stripping zone 27 is the region within separator column 28 wherein gasbubbles originating from analyte carrier stream 50 flow upwards to theliquid surface. The back pressure in separation vessel vapor outletstream 40 must be less than the hydrostatic head developed between theliquid surface and the bottom of separator column 28.

Referring again to FIG. 1, reagent is introduced into separator vessel20 through reagent inlet steam 32 from reagent reservoir 30. Reagentreservoir 30 is an airtight container into which batches of reagent canbe added. Additional reservoirs (not shown in FIG. 1) may be used tosupply various different reagent to separator vessel 20 depending on thetarget constituents to be volatilized. For target acid constituents,reagent may consist of, for example, a 10N aqueous solution of sulfuricacid which is used to maintain a pH in separator vessel 20 of less than2. For analysis of target base constituents, reagent may consist of, forexample, a 10N aqueous solution of sodium hydroxide for maintaining thepH of liquid inside separator vessel 20 above 12. Reagent dip tube 33 isan extension of reagent inlet stream 32 extending from the top ofreagent reservoir 30 down into the reservoir with an opening near thebottom. During normal operation, the liquid level of reagent in reagentreservoir 30 is maintained above the level of dip tube 33. Flow ofreagent into reagent dip tube 33 is achieved by introducing gaspropellant from a source not shown through propellant stream 36, whichis controlled by propellant pressure indicator and controller 34, intothe vapor space contained within reagent reservoir 30. By adding acontrolled volume of propellant gas into reagent reservoir 30, aconstant flow of reagent into separator vessel 20 is achieved.

Analyte carrier gas is introduced into separator vessel 20 throughanalyte carrier stream 50 which flows from a source not shown throughanalyte carrier stream flow indicator 54. The rate of flow of analytecarrier gas is controlled by analyte carrier stream flow controller 52.Nitrogen is but one gas which is suitable as analyte carrier gas.

Volatilized constituents and analyte carrier gas exit from separatorvessel 20 through separator vessel vapor outlet stream 40. Separatorvessel vapor outlet stream 40 flows through vapor filter 42, thenthrough first detector means 46, then through second detector means 48and finally to vapor vent 49. Vapor filter 42 removes liquid water fromvapor. Such filters are well known and commercially available. One suchfilter is the Model No. A944-BX, manufactured by Balston Filter Productsof Lexington, Mass. First detector means 46 is, for example, a hydrogensulfide analyzer based on spectrophotometric determinations made in theultraviolet wavelength region. In this example, first detector means 46is effective to determine the concentration of volatilized H₂ S inseparator vessel vapor outlet stream 40. This concentration can becorrelated to the concentration of H₂ S dissolved in the correspondingliquid sample. First signal line 60 is provided to pass a signalgenerated by first detector means 46 to processing means, not shown,wherein the concentration of constituents in said liquid stream can bedisplayed and used, for example, to control a process. Second detectormeans 48 is, for example, a CO₂ analyzer based on spectrophotometricdeterminations made in the infrared wavelength region. In this example,second detector means 48 is effective to determine the concentration ofCO₂ vapor in separator vessel vapor outlet stream 40. This concentrationcan be correlated to the concentration of CO₂ dissolved in thecorresponding liquid sample. Second signal line 62 is provided to pass asignal generated by second detector means 46 to processing means, notshown, which determines the concentration of constituents in said liquidstream.

The spectrophotometric detectors mentioned hereinabove measure theabsorbance of radiation energy by the volatilized constituents.Absorbance is the loss of radiation energy between the radiation sourceand a detector. The concentration of volatilized constituents is relatedto absorbance by Beer's Law:

    A=log I.sub.o /I=abc

where:

A is the absorbance

I_(o) is the amount of radiation detected absent analytes

I is the amount of radiation detected in the presence of analytes

a is the extinction coefficient of the analyte at a given wavelength

b is the cell pathlength (distance between source and detector), and

c is the concentration of analyte.

For values of A less than about 1.5, the relationship between c and A islinear. It is preferable, therefore, that the cell pathlengths in thedetectors 46 and 48 be adjusted so that the product abc over the rangeof interest of c will result in a value of A within the linear range.

Experimental determinations of H₂ S concentration made using anapparatus designed in accordance with the invention disclosed herein arepresented in FIG. 5. In this case, detector means 46 was used to measurethe concentration of H₂ S by weight in parts per million (ppm). Thenominal ppm of H₂ S present in the samples was known and is representedby ppm by weight along the X axis. The samples consisted of Na₂ S andNa₂ CO₃ in a mixture of NaOH and H₂ O. When the samples are reacted witha strong acid, H₂ S, CO₂ and NaSO₄ are produced. Samples containingvarying concentrations of H₂ S were measured, the determinations beingmade on different days at room temperature using the same analysisapparatus. Excellent correlation between nominal and detectedconcentrations of H₂ S can be clearly seen in FIG. 5. From this data itcan be concluded that using the apparatus described herein accurate,repeatable determinations of the amount of H₂ S in the sample can bemade.

Similarly, FIG. 6 represents determinations of CO₂ produced when samplesconsisting of Na₂ S and Na₂ CO₃ in a mixture of NaOH and H₂ O werereacted with a strong acid. Samples containing varying concentrations ofCO₂ were measured, the determinations being made on three separate daysat room temperature using the same apparatus. The Y axis represents thedetected concentration of CO₂ in ppm by weight using detector means 48.The X axis represents the nominal ppm of CO₂ by weight. Again, excellentcorrelation between nominal and detected concentrations of CO₂ isdemonstrated.

Significant improvements in the control of the amine systems can beachieved using the method and apparatus taught herein. Theseimprovements are attributable to (1) detection of total acid gasconcentration rather than just hydrogen sulfide concentration in sourgas, and (2) on-line detection of these constituents that are dissolvedin liquid amine streams.

Referring to FIG. 3, the level of H₂ S in fuel gas is controlled by theequilibrium established between lean (regenerated) amine entering thetop of amine contactor 102 through lean amine pump outlet 146 andsweetened gas exiting amine contactor 102 through sweet gas outlet 106.This equilibrium is a function of the temperature and pressure of aminecontactor 102, and the concentration of total acid gas (H₂ S and CO₂) inthe lean amine. High levels of acid gas in the fuel gas entering aminecontactor 102 through sour gas inlet 104 must be corrected by loweringthe temperature, raising the pressure, lowering the concentration ofacid gas in the lean amine, or increasing the flow rate of lean amine tothe contactor.

It is well known that H₂ S represents only a fraction of the total acidgas present in lean amine. However, it is standard in the industry tocontrol amine systems based on analysis for H₂ S only, even though totalacid gas is a better measure of lean amine quality. Referring to FIG. 4,a comparison is made therein of the steam rate necessary forregenerating rich amine versus (1) the concentration of acid gas, and(2) the concentration of H₂ S only in the lean amine. The data in FIG. 4was acquired during a week-long study of an actual amine unit. Inaccordance with normal operating procedures, samples of lean amine wereobtained and analyzed for H₂ S once per 8-hour shift. Stripping steamrates were also noted. For the purpose of the week-long study, totalacid gas concentration was also determined. This data shows that withinthe range of acid gas concentration between 600 and 1,200 grains pergallon, H₂ S only represents between 11% and 14% of total acid gas inlean amine. Further, the data shows that H₂ S concentration is notproportional to acid gas concentration at different steam rates. SinceCO₂, which represents most of the remaining acid gas, affects theabsorption of H₂ S from fuel gas, the importance of controllingregeneration steam rates using determinations of total acid gas in richamine is clear.

Referring again to FIG. 3, improved steam input control can be achievedby locating an apparatus as disclosed herein, rich amine analyzer 160,in contactor bottoms line 108 and using the signal generated therefromto control steam flow control valve 136. This is a form of feed forwardcontrol whereby information about the quality of rich (contaminated)amine being fed from the bottom of amine contactor 102 through contactorbottoms line 108, first heat exchange means 110, rich amine inlet 112into amine regenerator 120 is furnished to steam flow controller 162which in turn controls the flow of steam through steam inlet 128,reboiler steam coil 130 and condensate outlet 134. Reboiler 126 is usedto input energy into amine regenerator 120 by heating amine circulatedfrom amine regenerator 120 through reboiler inlet 124, reboiler 126 andback into amine regenerator 120 through reboiler outlet 132. When thelevel of acid gas concentration in contactor bottoms line 108 exceeds aset point level, steam flow controller 162 adjusts steam flow controlvalve 136 to increase the flow of steam and hence the energy input intoamine regenerator 120. Similarly, when the total acid gas concentrationof rich amine in contactor bottoms line 108 falls below a predeterminedset point, steam flow controller 162 adjusts steam flow control valve136 to restrict the flow of steam thereby reducing the amount of energyinput into amine regenerator 120.

Heat input into amine regenerator 120 liberates acids absorbed by theamine in amine contactor 102, thereby regenerating amine forrecirculation to amine contactor 102. Acid gases are removed from amineregenerator 120 through regenerator overhead line 122. Lean amine exitsamine regenerator 120 through lean amine line 140 and first heatexchange means 110. First heat exchange means 110 preheats rich amineand cools lean amine. Lean amine pump 144 is used to return the leanamine to amine contactor 102 through lean amine pump outlet 146 andsecond heat exchange means 148, which further cools the lean amine.

In addition to improved steam input control into amine regenerator 120by means of rich amine analyzer 160 due to determination of total acidgas concentration rather than just H₂ S concentration, improvements insteam control attributable to on-line responsiveness of rich amineanalyzer 160 should also be noted. At present, it is typical for steaminput into amine regeneration systems to be based upon H₂ Sdeterminations made in quality control laboratories once per operatingshift. Clearly, this is less desirable than control based on on-linemeasurements since quick response to variations in rich amine loadingare not possible using the former method.

Control of steam input into reboiler 126 can be further optimized bylocating an apparatus as disclosed herein in reboiler inlet line 124 andusing the signal generated therefrom to further control steam flowcontrol valve 136. This is a form of feedback control wherebyinformation about the quality of lean amine exiting amine regenerator120 is furnished to steam flow controller 162 which in turn controls theflow of steam through steam inlet 128, reboiler steam coil 130 andexiting through condensate outlet 134. In this way, steam flowcontroller 162 is provided information relative to the acid gas contentof rich amine being fed to amine regenerator 120 as well as the acid gasconcentration in lean amine exiting amine regenerator 120.

Further amine system control enhancement can be achieved by conservinglean amine contacted in amine contactor 102. The flow of lean amine intoamine contactor 102 is controlled by lean amine flow controller 166 inconnection with lean amine flow control valve 147. By measuring theconcentration of acid gas in contactor bottoms line 108 and using thisdetermination to control lean amine flow into amine contactor 102, therate of addition of lean amine to amine contactor 102 can be maintainedin proportion to rich amine loading. More particularly, the rate atwhich lean amine is supplied to amine contactor 102 can be balanced withthe amount of contaminants detected in contactor bottoms line 108 byrich amine analyzer 160. This is important since too much amine inputcan result in a product penalty in dissolved hydrocarbon. In addition,raw material will be wasted if more amine is degraded than necessary. Onthe other hand, understripping of amine that is recycled to aminecontactor 102 can result in a corrosion problem.

That which is claimed is:
 1. A method for on-line determination of theconcentration of target constituents in one or more liquid streamscontaining such constituents comprising:essentially continuously andrepetitively capturing a plurality of samples of substantially constantsize from the liquid stream or streams; passing said samplesindividually to a separation zone wherein succeeding samples arecontacted a reagent selected from the group consisting of strong acidsand strong bases at separation conditions thereby causing essentiallyall of the target constituents of each of said succeeding samples toreact with said reagent to form volatilized analytes; separating saidvolatilized analytes entrained in a liguid within said separation zoneby means of an analyte carrier stream which flows at a substantiallyconstant rate through said liquid so as to strip and carry awayessentially all of said volatilized analytes of each of said succeedingsamples from said liquid; and directing said analyte carrier stream fromsaid separation zone to a detection zone wherein signals are generatedwhich are proportional to the concentration of each target constituentcontained in said liquid stream or streams; determine the concentrationof each of said target constituent based upon said signalswherein saidtarget constituents are selected from at least one member of the groupconsisting of weak acids, weak bases, the soluble salts of weak acidsand the soluble salts of weak bases.
 2. The method of claim 1 whereinsaid samples from said liquid stream or streams are passed to saidseperation zone by injecting said succeeding samples individually into aseparate sample carrier stream which flows from a sample carrier fluidsource continuously into said separation zone.
 3. The method of claim 2,wherein said sample carrier stream comprises a fluid flowing at anessentially constant rate.
 4. The method of claim 3, wherein said samplecarrier stream fluid does not substantially chemically react with saidsamples.
 5. The method of claim 3, wherein said sample carrier streamfluid substantially chemically reacts with said samples.
 6. The methodof claim 3, wherein said sample carrier stream fluid is water.
 7. Themethod of claim 1, wherein said reagent is supplied continuously to saidseparation zone in a quantity sufficient to volatilize essentially allof the said target constituents of said individual succeeding samplesupon contact with said reagent.
 8. The method of claim 7, wherein saidtarget constituents are acids and said reagent comprises a strong acidfor the determination of the concentration of said target acidconstituents.
 9. The method of claim 8, wherein said reagent is aqueoussulfuric acid.
 10. The method of claim 8, wherein the pH of the liquidwithin said separation zone is maintained at a level not exceeding 2.11. The method of claim 8, wherein said target acid constituents areselected from at least one member of the group consisting of hydrogensulfide and carbon dioxide.
 12. The method of claim 7, wherein saidtarget constituents are bases and said reagent comprises a strong basefor the determination of the concentration of said of said target baseconstituents.
 13. The method of claim 12, wherein said reagent isaqueous sodium hydroxide.
 14. The method of claim 12, wherein the pH ofthe liquid within said separation zone is maintained at a level not lessthan
 12. 15. The method of claim 12, wherein said target baseconstituent comprises ammonia.
 16. The method of claim 1, wherein saidanalyte carrier stream comprises a substantially continuously flowinganalyte carrier gas which is supplied to said separation zone atessentially a constant flow rate, said analyte carrier gas is used tostrip entrained volatilized analyte from said liquid and to carry suchstripped volatilized analyte produced by said succeeding samples awayfrom said separation zone to said detection zone.
 17. The method ofclaim 16, wherein said analyte carrier gas is a gas that does notsubstantially chemically react with the liquid within said separationzone.
 18. The method of claim 16, wherein said analyte carrier gas is agas that substantially chemically reacts with the target constituentswithin said separation zone to enhance detectability of theconstituents.
 19. The method of claim 1, wherein said volatilizedanalytes from said succeeding individual samples pass to one or moredetectors within said detection zone, at least one of said detectorsconstructed so as to measure separately the concentration of eachindividual target constituent.
 20. The method of claim 19, wherein saiddetectors are spectrophotometric devices for measuring the absorbance ofradiation energy by said volatilized analytes.
 21. The method of claim19, wherein said detectors are constructed so as to measure variationsin conductivity of liquids of said volatilized analytes.
 22. The methodof claim 19, wherein said detector or detectors is essentiallycontinuously monitored by:determining a baseline value for each saiddetector or detectors in the presence of said analyte carrier gas alone;repetitively passing volatilized analytes from succeeding individualsamples past said detector or detectors by means of an essentiallycontinuously flowing stream of said analyte carrier stream to determinethe concentration of said analytes; and verifying substantial identitybetween said baseline value for each said detector or detectors and theactual value determined by detector after volatilized analytes from onesample have fully passed from said detector or detectors but prior tothe introduction to said detector or detectors of the volatilizedanalytes of succeeding samples.
 23. A method for on line determinationof the concentration of weak acid constituents in one or more liquidamine streams in a gas sweetsning process comprising:essentiallycontinuously and repetitively capturing a plurality of samples ofsubstantially constant size from the liquid amine stream or streams;passing said samples individually to a separation zone whereinsucceeding samples are contacted with a reagent comprising a strong acidat separation conditions thereby causing essentially all of the weakacid constituents of each of succeeding said samples to react with saidreagent to form volatilized analytes; separating said volatilizedanalytes entrained in a liquid within said separation zone with ananalyte carrier stream which flows at a substantially constant ratethrough said liquid so as to strip and carry away essentially all of theweak acid constituents of each of said succeeding samples from saidliquid; and directing said analyte carrier stream from said separationzone to a detection zone wherein signals are generated which areproportional to the concentration of each weak acid constituentcontained in said liquid amine stream or streams; determine theconcentration of each weak acid constituents based on saidsignalswherein said weak acid constituents are selected from at leastone member of the group consisting of hydrogen sulfide, carbon dioxide,the soluble salts of hydrogen sulfide and the soluble salts of carbondioxide.
 24. The method of claim 23, wherein said samples from saidliquid amine stream or streams are passed to said separation zone byinjecting said succeeding samples individually into a separate carrierstream comprising a fluid that flows at a constant rate from a samplecarrier fluid source into said separation zone.
 25. The method of claim24, wherein said sample carrier stream fluid is water.
 26. The method ofclaim 23, wherein said reagent comprises a strong acid which is suppliedcontinuously to said separation zone at a rate and strength which uponcontact will volatize essentially all of said weak acid constituents ofeach of said succeeding samples.
 27. A method for on line determinationof the concentration of ammonia in one or more water influent streams ina waste water process comprising:essentially continuously andrepetitively capturing a plurality of samples of substantially constantsize from said water influent stream or streams; passing said samplesindividually to a separation zone wherein succeeding samples arecontacted with a reagent at separation conditions thereby causingessentially all of the ammonia of each of said succeeding samples toreact with said reagent to form volatilized analytes; separating saidvolatilized analytes entrained in a liquid within said separation zonewith an analyte carrier stream which flows at a substantially constantrate through said liquid so as to strip and carry away essentially allof the ammonia of each of said succeeding samples from said liquid; anddirecting said analyte carrier stream from said separation zone to adetection zone wherein signals are generated which are proportional tothe concentration of ammonia contained in said water influent stream orstreams; determine the concentration of ammonia based upon said signal.28. The method of claim 27, wherein said samples from said waterinfluent stream or streams are passed to said separation zone byindividually injecting said succeeding samples into a separate samplecarrier stream comprising a fluid that flows at a constant rate from asource into said separation zone.
 29. The method of claim 28, whereinsaid sample carrier stream fluid is water.
 30. The method of claim 28,wherein said reagent comprises a strong base which is suppliedcontinuously to said separation zone at a rate and strength which uponcontact will volatilize essentially all of said weak base constituentsof each of said succeeding samples.
 31. A method for on-linedetermination of the concentration of target constituents in one or moreliquid streams containing such constituents comprising:essentiallycontinuously and repetitively capturing a plurality of samples ofsubstantially constant size from the liquid stream or streams; passingsaid samples individually to a separation zone wherein succeedingsamples are contacted with a reagent at separation conditions therebycausing essentially all of the target constituents of each of saidsucceeding samples to react with said reagent to form volatilizedanalytes; separating said volatilized analytes entrained in a liquidwithin said separation zone with an analyte carrier stream which flowsat a substantially constant rate through said liquid so as to strip andcarry away essentially all of said volatilized analytes of each of saidsucceeding samples from said liquid wherein said analyte carrier streamcomprises a substantially continuously flowing analyte carrier gas whichis supplied to said separation zone at essentially a constant flow rate,said analyte carrier gas is used to strip entrained volatilized analytefrom said liquid and to carry said stripped volatilized analyte producedby said succeeding samples away from said separation zone and whereinsaid analyte carrier gas substantially chemically reacts with saidtarget constituents within said separation zone to enhance detectabilityof said constituents; and directing said analyte carrier stream fromsaid separation zone to a detection zone wherein signals are generatedwhich are proportional to the concentration of each target constituentcontained in said liquid stream or streams; determine the concentrationof ammonia based upon said signalswherein said target constituents areselected from at least one member of the group consisting of weak acids,weak bases, the soluble salts of weak acids and the soluble salts ofweak bases.